By appropriate pretreatment with a modifier, a heterogeneous catalyst can be endowed with high specificity for the synthesis of a selected isomer in a single-step hydrogenation or dehydrogenation reaction. The catalyst surface behaves as if covered with a molecular template that determines the structure of the reaction product. We have used such catalysts to synthesize specific geometric isomers of simple alkenes and to induce optical activity in a prochiral heterocyclic compound. Our proposed research is aimed at extending the use of such catalyst systems to more complex stereospecific syntheses. Specifically, we intend to develop templated catalysts that can be used to place or remove double bonds in selected locations in organic compounds of biological interest.